This invention relates to the field of implantable devices. More particularly, it relates to detaching the implantable device from the delivery mechanism using low frequency energy or direct current (DC) to melt or sever the polymeric junction between the device and delivery mechanism.
There are a variety of implantable devices that require precise placement within the vasculature of the human body. Such devices include vaso-occlusive coils, stents and other three-dimensional devices. Vaso-occlusive coils are described, for example, in U.S. Pat. No. 4,994,069, to Ritchart et al.; U.S. Pat. No. 5,624,461 to Mariant; U.S. Pat. No. 5,639,277 to Mariant et al. and U.S. Pat. No. 5,649,949 to Wallace et al. describes variable cross-section conical vaso-occlusive coils. Stents are described, for example, in U.S. Pat. No. 4,655,771 to Wallsten; U.S. Pat. No. 4,954,126 to Wallsten and U.S. Pat. No. 5,061,275 to Wallsten et al.
Typically, implantable devices include a detachment mechanism in order to be released from the deployment mechanism (e.g., attached wire). Several classes of techniques have been developed to enable more accurate placement of implantable devices within a vessel. One class involves the use of electrolytic means to detach the vasoocclusive member from the pusher. In one technique (U.S. Pat. No. 5,122,136 to Guglielmi et al.) the vasoocclusive member is bonded via a metal-to-metal joint to the distal end of the pusher. The pusher and vasoocclusive member are made of dissimilar metals. The vasoocclusive member-carrying pusher is advanced through the catheter to the site and a low electrical current is passed through the pusher-vasoocclusive member assembly. The current causes the joint between the pusher and the vasoocclusive member to be severed via electrolysis. The pusher may then be retracted leaving the detached vasoocclusive member at an exact position within the vessel. In addition to enabling more accurate vasoocclusive member placement, the electric current may facilitate thrombus formation at the vasoocclusive member site. The only perceived disadvantage of this method is that the electrolytic release of the vasoocclusive member requires a period of time so that rapid detachment of the vasoocclusive member from the pusher does not occur. Other examples of this technique can be found in U.S. Pat. No. 5,423,829 to Pham et al. and U.S. Pat. No. 5,522,836 to Palermo.
Other forms of energy are also used to sever sacrificial joints that connect pusher and vasoocclusive member apparatus. An example is that shown in Japanese Laid-Open Patent Application No. 7-265431 or corresponding U.S. Pat. No. 5,759,161 and U.S. Pat. No. 5,846,210 to Ogawa et al. A sacrificial connection member, preferably made from polyvinylacetate (PVA), resins, or shape memory alloys, joins a conductive wire to a detention member. Upon heating by a monopolar high frequency current, the sacrificial connection member melts, severing the wire from the detention member. U.S. Pat. 5,944,733 to Engelson describes application of radiofrequency energy to sever a themoplastic joint.
In U.S. Pat. No. 4,735,201 to O""Reilly, an optical fiber is enclosed within a catheter and connected to a metallic tip on its distal end by a layer of hot-melt adhesive. The proximal end of the optical fiber is connected to a laser energy source. When endovascularly introduced into an aneurysm, laser energy is applied to the optical fiber, heating the metallic tip so as to cauterize the immediately surrounding tissue. The layer of hot-melt adhesive serving as the bonding material for the optical fiber and metallic tip is melted during this lasing, but the integrity of the interface is maintained by application of back pressure on the catheter by the physician. When it is apparent that the proper therapeutic effect has been accomplished, another pulse of laser energy is then applied to once again melt the hot-melt adhesive, but upon this reheating the optical fiber and catheter are withdrawn by the physician, leaving the metallic tip in the aneurysm as a permanent plug.
Other methods for placing implantable devices within the vasculature utilize heat releasable bonds that can be detached by using laser energy (see, U.S. Pat. No. 5,108,407). EP 0 992 220 describes an embolic coil placement system which includes conductive wires running through the delivery member. When these wires generate sufficient heat, they are able to sever the link between the embolic coil and the delivery wires. Further, U.S. Ser. No. 09/177,848 describes the use of fluid pressure (e.g., hydraulics) to detach an embolic coil.
A variety of mechanically detachable devices are also known. For instance, U.S. Pat. No. 5,234,437, to Sepetka, shows a method of unscrewing a helically wound coil from a pusher having interlocking surfaces. U.S. Pat. No. 5,250,071, to Palermo, shows an embolic coil assembly using interlocking clasps mounted both on the pusher and on the embolic coil. U.S. Pat. No. 5,261,916, to Engelson, shows a detachable pusher-vaso-occlusive coil assembly having an interlocking ball and keyway-type coupling. U.S. Pat. No. 5,304,195, to Twyford et al., shows a pusher-vasoocclusive coil assembly having an affixed, proximally extending wire carrying a ball on its proximal end and a pusher having a similar end. The two ends are interlocked and disengage when expelled from the distal tip of the catheter. U.S. Pat. No. 5,312,415, to Palermo, also shows a method for discharging numerous coils from a single pusher by use of a guidewire which has a section capable of interconnecting with the interior of the helically wound coil. U.S. Pat. No. 5,350,397, to Palermo et al., shows a pusher having a throat at its distal end and a pusher through its axis. The pusher sheath will hold onto the end of an embolic coil and will then be released upon pushing the axially placed pusher wire against the member found on the proximal end of the vaso-occlusive coil.
None of these documents disclose devices having detachment junctions that are detachable by applying low frequency or direct current.
The present invention includes compositions and methods for detaching implantable devices from deployment mechanisms using low-frequency energy or direct current.
In one aspect, the invention includes an assembly comprising (a) an implantable device; (b) a deployment mechanism; and (c) a junction member linking the implantable device and deployment mechanism. The junction member is detached from the implantable device by application of low-frequency energy or direct current, for example a thermoplastic polymer such as PVA. In certain embodiments, the low frequency or direct current is less than 100 kHz, preferably less than 80 Hz. The deployment mechanism can comprise, for example, a conductive wire. The implantable device can comprise, for example, a vasoocclusive coil or a stent.
In other aspects, any of the devices and/or assemblies described herein further include a source of low frequency energy or direct current attached to the delivery mechanism and/or a conductive member in operable contact with the junction member. In other embodiments, the assembly devices described herein further comprise a catheter, said assembly being disposed within the catheter. Further, the catheter may include a negative electrode at the distal tip of the catheter.
In other aspects, methods of using the assembly devices are provided, for example introducing an assembly as described herein into a subject and detaching the implantable device in the desired location by applying low frequency energy or direct current.
These and other embodiments of the subject invention will readily occur to those of skill in the art in light of the disclosure herein.